Evaluation of Dihedral Angles of Peptides Using IR Bands of Two Successive Isotope Labeled Residues

Abstract

The infrared (IR) absorption bands due to peptide bonds (amide bands) have long been used to determine the secondary structure of a peptide and to analyze intra- and intermolecular interactions between amides. In the present study, the dihedral angles of a residue in peptides have also been evaluated using the amide I IR band of two successive residues with isotope labeling. The two successive residues labeled with the C-13 and O-18 isotopes give the doublet amide I IR band and the intensity ratio (R-int) and the difference in peak position (Delta nu) of the doublet band were analyzed using GF matrix and ab initio molecular orbital calculations. We obtained the two-dimensional calculation maps of R-int and Delta nu against the two dihedral angles. The crossing point of the curves of R-int and Delta nu is the two dihedral angles of the measured residue. The evaluated dihedral angles of the simple peptides are compared with the reported values. We discuss the limitation and the application of the present method to biopolymers from the obtained results.